Organic electrophotographic photosensitive members (hereinafter “electrophotographic photosensitive members”) have been widely available on the market with rapidly spreading use of devices such as copiers and laser beam printers. A typical electrophotographic photosensitive member includes an undercoat layer containing metal oxide particles and a photosensitive layer formed on the undercoat layer.
The undercoat layer can contain a thermosetting resin, rather than an alcohol-soluble resin, as a binder resin for reduced dependence on ambient conditions such as temperature and humidity.
It is also known that the surface of the metal oxide particles contained in the undercoat layer can be treated with a silane compound (silane coupling agent) for improved electrophotographic properties and reduced dependence on ambient conditions of the electrophotographic photosensitive member.
Silane coupling agents have a silicon atom to which one to three hydrolyzable groups are attached. Often, silane coupling agents having a silicon atom to which three hydrolyzable groups are attached are used for electrophotographic photosensitive members. NPL 1 discloses the treatment effect and waterfastness of silane coupling agents with varying numbers of hydrolyzable groups. This literature shows that, of silane coupling agents having a 3-methacryloxy group and one to three hydrolyzable groups, i.e., chloro groups, those having three hydrolyzable groups produce the greatest treatment effect.
PTL 1 discloses an undercoat layer containing a binder resin and metal oxide particles whose surface is treated with a coupling agent having a substituted or unsubstituted amino group (silane coupling agent having a divalent group represented by —NH—). The binder resin used in PTL 1 is a polyamide resin. Polyamide resins tend to cause potential variation with ambient changes because of their high water absorbency, particularly under a high-temperature, high-humidity environment or a low-temperature, low-humidity environment.
PTL 2 discloses an undercoat layer for electrophotographic photosensitive members that contains a thermosetting resin and metal oxide particles. The thermosetting resin is an urethane resin, specifically, an urethane resin obtainable by polymerization of an isocyanate compound and a polyvinyl acetal resin. The metal oxide particles are treated with a coupling agent having an amino group (silane coupling agent having a divalent group represented by —NH—). As disclosed, this reduces an increase in residual potential after repeated use of electrophotographic photosensitive members or with ambient changes.